Binocular cyclotorsion in superior vestibular neuritis

Abstract

Conjugated cyclotorsion of the eyes toward the affected side can commonly be observed in vestibular neuritis. The aim of this study was to assess the differences in cyclotorsion between the ipsi- and contralesional eye during selective involvement of the superior branch of the vestibular nerve. We studied binocular cyclotorsion through ocular fundus photographs in 10 patients affected by acute superior vestibular neuritis (SVN). Cyclotorsion was also studied in 20 normal subjects. All SVN patients showed an ipsilesional cycloversion of the eyes. Normal subjects exhibited a constant mild excyclovergence (6.42 ± 2.34°). In SVN patients, contralateral incyclotorsion (8.4 ± 8.14°) was lower and not normally distributed compared to ipsilateral eye excyclotorsion (17.9 ± 4.36°) with no correlation between them. The interocular difference in cyclodeviation could be related to the starting physiological excyclovergence, to different tonic effects on the extraocular muscles of the two eyes and to the different influence of spontaneous nystagmus on cyclodeviation in the two eyes. We recommend referring only to ipsilateral excyclotorsion in the evaluation of utricular function during SVN and its subsequent compensation. Further studies are required to determine the binocular cyclotorsion in the case of other kinds of selective involvement of the vestibular nerve.